Hexane conversion

ABSTRACT

A process for producing isopentane which comprises: (a) isomerizing a C6-rich hydrocarbon fraction in an isomerization zone to obtain at least isopentane and C4 alkanes, (b) fractionating the isopentane from the C4 alkane to obtain an isopentane product, (c) disproportionating at least a portion of the C4 alkanes in a C4 disproportionation zone to obtain at least n-pentane and C3 hydrocarbons, and (d) isomerizing the n-pentane in the isomerization zone. Preferably, the isomerization zone uses a sulfactive isomerization catalyst so that the isomerization zone serves not only an isomerization function but also a purification function for subsequent disproportionation.

[ 1 Feb. 27, 1973 HEXANE CONVERSION [75] Inventors: Jacob D. Kemp, El Cerrito; Robert P. Sieg, Piedmont, both of Calif.

[73] Assignee: Chevron Research Company, San

Francisco, Calif.

22 Filed: Jan. 18,1971

21 Appl. 1%.; 107,202

[52] U.S. Cl. ..260/676 R, 260/683 D, 260/683.65

3,676,522 7/1972 Sieg ..260/683.65

Primary Examiner-Delbert E. Gantz Assistant Examiner.l. M. Nelson Attorney-G. F. Magdeburger, R. H. Davies, T. G. De .longhe and J. A. Buchanan, Jr.

[5 7] ABSTRACT A process for producing isopentane which comprises: (a) isomerizing a C -rich hydrocarbon fraction in an isomerization zone to obtain at least isopentane and C alkanes, (b) fractionating the isopentane from the C alkane to obtain an isopentane product, (c) disproportionating at least a portion of the C alkanes in a C disproportionation zone to obtain at least n-pentane and C hydrocarbons, and (d) isomerizing the n-pentane in the isomerization zone. Preferably, the isomerization zone uses a sulfactive isomerization catalyst so that the isomerization zone serves not only an isomerization function but also a purification function for subsequent disproportionation.

12 Claims, 1 Drawing Figure [51] Int. Cl ..C07c 9/00 [58] Field of Search ..260/676, 683 D, 683.65

[56] References Cited UNITED STATES PATENTS 2,951,888 9/1960 Carr ..260/683.65 3,409,682 11/1968 Mitsche ..260/666 3,507,931 4/1970 Morris et a1. ...260/683.65 3,445,541 5/1969 Heikelsberg... .....260/683 D 3,392,212 7/1968 DOuville ...260/683.73 3,301,917 1/1967 Wise ...260/683.65 3,516,925 6/1970 Lawrence et al ..208/211 iCA DISPROPORTIONATION ISOPENTANE PRODUCT FRACTIONATION ZONE ISOMERIZATION nC5,iCe.nCa

c1+ TO CAT REFORMING HEXANE CONVERSION BACKGROUND OF THE INVENTION The present invention relates to a combination process involving isomerization of saturated hydrocarbons. More particularly, the present invention relates to isomerization operated in combination with saturated hydrocarbon disproportionation, and preferably with integrated common fractionation facilities.

lsomerization is a well-known and frequently used step in petroleum refining. It enables the adjustment of the octane number upwards by converting normal paraffins, such as normal hexane, to isoparaffins, such as 2,2-dimethylbutane. A blend of various isomeric paraffins provides a gasoline which has a higher octane number than a gasoline consisting of normal paraffins. lsomerization is generally performed by passing isomerizable hydrocarbons together with hydrogen through a reaction zone containing an isomerizationcatalyst. The hydrogen-to-hydrocarbon mol ratio varies within a wide range, generally from 0.05:1 to :1, preferably within the range of about 0.5:1 to 2:1 for pentanes and hexanes and 0. l :1 to 1:1 for butanes. The reaction temperature will depend upon the specific hydrocarbons being isomerized and the nature and type of catalyst employed. Hydrocarbon streams consisting chiefly of pentanes and hexanes are usually isomerized at temperatures within the range of 200-900F. The isomerization, normally effected under pressure, may be carried out in the liquid or vapor phase. Generally, pressures within the range of 300-],000 psig have been used. A liquid hourly space velocity (LHSV), that is, the volume of liquid charged per hour per volume of catalyst, within the range of 0.5 to 10.0 and preferably within the range of about 0.75 to 4.0 is employed.

Various catalysts have been suggested for use in isomerization processes. In general, the isomerization can be effected at low temperatures (ca. 300F.) with a Friedel-Crafts catalyst, such as aluminum chloride, or at high temperatures (ca. 750F.) with a supported metal catalyst, such as platinum on halogenated alumina or silica-alumina. Thermodynamic equilibrium for isoparaffins is more favorable at low temperatures; however, the low-temperature-process has not received wide application because the Friedel-Crafts catalyst is quite corrosive and therefore expensive metals or alloys must be used. 0f the high temperature isomerization processes, the noble metal catalysts such as platinum or palladium are perhaps considered to be the most effective.

As indicated in U.S. Pat. Nos. 2,951,888 and 3,472,912, minor amounts of sulfur compounds in the feed to isomerization processes are harmful for the typical isomerization processes. Catalysts used in typical isomerization processes include composites of a hydrogenating component on an amorphous acidic silica-alumina support and more usually composites comprising halogenated alumina or aluminum, either of which latter composites are herein referred to as halogenated aluminum catalysts.

According to U.S. Pat. No. 2,951,888, a C -C paraffinic feedstock is desulfurized to a sulfur content less than 1 ppm so that, better results are achieved in hydroisomerization of the paraffinic feedstock with a catalyst selected from the group consisting of nickel, nickel-molybdenum, and palladium, supported on an acidic silica-alumina support containing 50-90 percent silica, at a temperature of 650800F., pressure of l00l,000 psig, and hydrogen-hydrocarbon mol ratio of 0.5-5 .0.

U.S. Pat. No. 3,472,912 also discloses an over-all combination process involving hydrotreating and isomerization wherein a nickel molybdenum-on-alumina catalyst is used under hydrotreating conditions to remove sulfur from C -C saturated hydrocarbons so that the hydrocarbons can be isomerized with increased life for the isomerization catalyst. Preferred isomerization catalysts according to the process of U.S. Pat. No. 3,472,912 are platinum-alumina composites activated by the addition of carbon tetrachloride (thereby resulting in a catalyst which is herein classified as a catalyst containing halogenated aluminum).

Recently, catalysts comprising either natural or synthetic crystalline aluminosilicates have been suggested for isomerization processes. Included among the crystalline aluminosilicates which have been suggested are the type X and type Y silicates, mordenite, and layered aluminosilicates such as described in Granquist U.S. Pat. No. 3,252,757.

U.S. Pat. No. 3,507,931, titled isomerization of Paraffinic Hydrocarbons in the Presence of a Mordenite Catalyst discloses the isomerization of straight run distillates rich in C C normal paraffins using a catalyst having a high silica-to-alumina ratio, preferably above 20:1, and operating the isomerization reaction at relatively low temperatures, such as 250400F.

U.S. Pat. Nos. 3,280,212 and 3,301,917 also disclose hydroisomerization processes using crystalline aluminosilicate-type catalysts.

As indicated above, the present invention is directed to both isomerization and disproportionation.

The term disproportionation is used herein to mean the conversion of hydrocarbons to new hydrocarbons of both higher and lower molecular weight. For example, butane may be disproportionated according to the reaction:

As can be seen from the above disproportionation reaction, the butane is in part converted to a higher molecular weight hydrocarbon, namely, pentane. Various processes have been suggested for converting hydrocarbons to higher molecular weight hydrocarbons.

U.S. Pat. No. 1,687,890 is directed to a process of converting low-boiling-point hydrocarbons into higherboiling-point hydrocarbons by mixing a hydrocarbon vapor with steam and then contacting the steamhydrocarbon mixture with iron oxide at temperatures in excess of 1,112F. It is theorized in U.S. Pat. No. 1,687,890 that the following reactions may be involved to a greater or lesser extent:

1. Paraffin hydrocarbons on being brought into contact with ferric oxide at elevated temperatures are oxidized or dehydrogenated, forming unsaturated hydrocarbons.

2. Unsaturated hydrocarbons of low molecular weight polymerize into unsaturated hydrocarbons of higher molecular weight when subjected to elevated temperatures, the extent of polymerization depending upon the temperature and duration of treatment.

"7. Unsaturated hydrocarbons are hydrogenated by nascent hydrogen."

Another process which has been proposed for converting hydrocarbons to higher molecular weight hydrocarbons is olefin disproportionation. Numerous methods and catalysts have been disclosed for the disproportionation of olefins. In most of these processes, the olefin is disproportionated by contacting with a catalyst such as tungsten oxide or molybdenum oxide on silica or alumina at a temperature between about l50l,l00F. and at a pressure between about 15 and 1,500 psia. These prior art processes have been directed to an effective method to convert essentially only olefins, not saturated hydrocarbons, to higher molecular weight hydrocarbons by disproportionation.

For example, in U.S. Pat. No. 3,431,316, an olefin disproportionation process is disclosed, and it is stated that, if desired, paraffmic and cycloparaffinic hydrocarbons having up to 12 carbon atoms per molecule can be employed as diluents for the reaction; that is, the saturated hydrocarbons are non-reactive and merely dilute the olefins which are the reactants.

A process for the direct conversion of saturated hydrocarbons to higher molecular weight hydrocarbons would be very attractive because in many instances saturated hydrocarbons are available as a relatively cheap feedstock. For example, in many instances, excess amounts of propane and/or butanes are available in an overall refinery operation.

Processes which have been previously reported wherein saturated hydrocarbons are disproportionated include contact of saturated hydrocarbons with solid catalyst comprised of AlCl on M and contact of saturated hydrocarbons with a promoter comprised of alkyl fluoride and BF The use of the AlCl solid catalyst was uneconomic because, among other reasons, the catalyst was non-regenerable. The use of alkyl fluoride and BE, was unattractive because of severe corrosion, sludge formation and other operating problems.

In the past it has been the practice to convert saturated hydrocarbons, particularly normal alkanes, to olefins as a separate or distinct step and then to disproportionate the olefins to valuable higher niolecular weight hydrocarbons.

For example, in U.S. Pat. No. 3,431,316, saturated light hydrocarbons are cracked to form olefins, and then the olefins are separated from the cracker effluent and fed to a disproportionation zone wherein the olefins are disproportionated to higher molecular weight hydrocarbons. Thus, a separate step is used to obtain olefins because, according to the prior art, no economically feasible process is available for the direct disproportionation of saturated hydrocarbons.

U.S. Pat. No. 3,445,541 discloses a process for the dehydrogenation-disproportionation of olefins and paraffims, using a combined dehydrogenation and disproportionation catalyst. According to U.S. Pat. No. 3,445,541, a hydrocarbon feed which is either an acyclic paraffin or acyclic olefin having three to six carbon atoms is contacted with the catalyst at conditions of temperature and pressure to promote dehydrogenation and disproportionation. It is said that the process can be carried out at temperatures between 800F. and 1,200F.; however, the lowest temperature used for processing a paraffin in accordance with any of the examples of U.S. Pat. No. 3,445,541 is 980F., and typically the temperature used is between 1,040F. and 1,125F.

The high-temperature process disclosed in U.S. Pat. No. 3,445,541 is shown therein to result in only relatively low yields of saturated higher molecular weight hydrocarbons. The U.S. Pat. No. 3,445,541 process operates with a substantial amount of olefins in the reaction zone and with about 10 to 50 volume percent or more olefins in the effluent from the disproportionation reaction :gone. U.S. Pat. No. 3,445,541 does not disclose or suggest any advantages for disproportionation of hexanes and butanes in combination with C and C isomerization.

SUMMARY OF THE INVENTION According to the present invention, a process is provided for producing isopentane which comprises: (a) isomerizing a C -rich hydrocarbon fraction in an isomerization zone to obtain at least isopentane and C alkanes, (b) fractionating the isopentane from the C alkanes to obtain an isopentane product, (c) disproportionating at least a portion of the C alkanes in a C disproportionation zone to obtain at least n-pentane and C hydrocarbons, and (d) isomerizing the n-pentane in the isomerization zone.

The process of the present invention results in the production of high-octane isopentane from low-octane hexane (such as normal hexane, which has an octane rating of about 26). The isopentane which is produced in the process of the present invention has an octane rating of about 92 and is particularly useful in high-octane unleaded or low-head-content gasolines.

Isomerization of C hydrocarbons can be used to upgrade the octane rating of normal hexane-rich hydrocarbon fractions. However, the octane can be increased only to about -75 (motor octane) by isomerization because the main hexane isomers produced, namely, Z-methyl pentane and 3-methyl pentane, have an octane rating of only 73 and 75, respectively. Although increasing the octane rating of a C fraction from the vicinity of about 26, which is the octane of normal hexane, to about 70-75 by isomerization to produce isohexanes represents a substantial increase, it is generally not a sufficient increase to produce highoctane gasoline components for use in unleaded or lead-free gasolines.

The C -rich hydrocarbons also have been considered as feedstocks for catalytic reforming in order to reform the C material into reasonably low volatility gasoline boiling range hydrocarbons in the octane range. However, the C hydrocarbons have been found to make a relatively unattractive feedstock for catalytic reforming processes.

Thus, it is desirable to provide a process for upgrading C -rich hydrocarbon fractions into 90+ octane rating components. The process of the present invention achieves these desired results by the combination of isomerization with disproportionation. In addition, the isomerization step is particularly advantageously employed with the disproportionation step in the present invention as the isomerization step serves the dual function of (l) purifying C -rich hydrocarbons which are subsequently disproportionated, and (2) isomerizing a portion of the C hydrocarbons.

disproportionation zone is sensitive to even small amounts of H 8, and H 8 will be formed in the disproportionation zone unless the organic sulfur compounds are substantially completely removed ahead of the disproportionation zone.

Also, the isomerization zone can serve to increase the amount of isopentane produced in the disproportionation zone by providing a branched-chain C feed for the disproportionation zone. Using the preferred dual-function dehydrogenation-olefin disproportionation catalyst for the disproportionation zone, there is substantially no production (or depletion) of branchedchain hydrocarbons in the disproportionation reaction zone.

According to a preferred embodiment of the present invention, the isomerization zone is further integrated with the disproportionation zone by using common fractionation facilities, at least in part. The term fractionation facilities is used herein to mean distillation columns or the like and associated equipment.

The effluent from the C -C isomerization zone is usually composed primarily of isobutane, normal butane, isopentane, normal pentane, isohexanes and normal hexane. However, there also is present minor or small amounts of propane and C hydrocarbons. It will, of course, be understood that the amount of these secondary hydrocarbons will depend upon several factors, including the composition of the feed to the isomerization zone, the type catalyst used in the isomerization zone (some isomerization catalysts have higher per-pass conversions but lower selectivities to the desired isopentane and isohexane products), and the temperature used in the isomerization zone (higher temperatures usually resulting in more light hydrocarbons such as propane). The effluent hydrocarbons from normal butane disproportionation according to the preferred embodiments of the present invention using the two-component disproportionation catalyst usually are primarily propane, normal butane, normal pentane, normal hexane and C,+ hydrocarbons. However, there will also be minor or small amounts of isobutane, isopentane, and isohexane. The amounts of these isoor branched-chain hydrocarbons will increase if increased amounts of isobutane are fed to the C disproportionation step. Thus, it is particularly advantageous to use common fractionation facilities for the isomerization zone effluent hydrocarbons and the disproportionation zone effluent hydrocarbons when substantial amounts, for example more than 5 or 10 weight percent, isobutane is fed to the C, disproportionation zone because, in this instance, there is an increased amount of common hydrocarbons from both the isomerization zone and the disproportionation zone.

The fractionation facilities required for the effluent from the isomerization zone and for the effluent from the disproportionation zone can range from one or two columns up to about eight sequential columns. For example, a propane splitter to separate propane from isobutane+; an' isobutane splitter to separate isobutane from normal butane-F; a normal butane splitter to separate normal butane from isopentane+; an isopentane splitter to separate isopentane from n-pentane+; a normal pentane splitter to separate normal pentane from isohexane+; an isohexane splitter to separate isohexane from normal hexane+; and a normal hexane splitter to separate normal hexane from C The fractionation of the aforementioned hydrocarbon cuts can be carried out in sequential separate columns or, at the other extreme, one column can be used similar to crude oil distillation with side streams being withdrawn from the column and stripped, if necessary. As indicated previously, the amounts of the various components present in the effluents from the isomerization zone and the disproportionation zone can vary. Thus, in some instances, only part of the fractionation for the two zones will be carried out in common fractionation facilities with the other part being carried out in separate fractionation facilities for the respective zones. Because there are usually substantial amounts of normal pentane and C alkanes in the effluent hydrocarbons in both the isomerization zone and the disproportionation zone, it is particularly preferred to carry out'the separation of normal pentane from C alkanes in a distillation column common to both the isomerization zone and the disproportionation zone.

In the process of the present invention, the feed to the C disproportionation zone can be a normal butane feed or a feed containing substantial amounts of isobutane in addition to normal butane. Usually it is preferred to feed isobutane as well as the normal butane to the disproportionation zone so as to produce isopentane (as well as normal pentane from the normal butane). lsopentane has a substantially higher octane than the isohexanes Z-methyl pentane and 3-methyl pentane, which are the primary isohexane products from C isomerization using sulfactive isomerization catalysts and isomerization conditions (500800F.) suitable for hydrodesulfurization.

As indicated above, one of the important purposes which the isomerization zone serves in the process of the present invention is to remove sulfur impurities from the C fraction before the butanes are fed to the disproportionation zone. In broad scope, the process of the present invention can be applied to the isomerization and subsequent disproportionation of C,, -rich hydrocarbon streams which are essentially free of sulfur impurities as, for example, C hydrocarbons contained in C hydrocarbon streams obtained from a catalytic reforming unit. However, the process combination of the present invention has particular advantage when applied to C -rich hydrocarbon streams containing minor amounts of sulfur impurities, usually at least 5 ppm sulfur.

C hydrocarbon cuts obtained by crude oil distillation, i.e., straight run C -rich hydrocarbon fractions, contain usually at least 5 ppm organic sulfur compounds (calculated as elemental sulfur by weight) and generally between about 20 and 500 ppm organic sulfur compounds. The isomerization zone can use a hydrotreating step ahead of the isomerization reaction zone catalyst as in the case of using halogenated aluminum-type catalysts, but it is preferred in the process of the present invention to use a crystalline aluminosilicate-type hydroisomerization catalyst, many of which catalysts we have found can be operated with several hundred ppm sulfur and frequently up to about 500 or 1,000 ppm sulfur in the feed without substantially decreasing the life of the hydroisomerization catalyst. Also, the crystalline aluminosilicate-type catalyst can be used to obtain relatively high yields of isohexane per pass at temperatures usually about 100F. less than is required for a comparable isohexane yield using halogenated aluminum-type isomerization catalysts. Halogenated aluminum-type catalysts which are sensitive to sulfur poisons and thus not as preferred for use in the process of the present invention include the catalyst such as used in the butamer process described in the Oil and Gas Journal, Vol. 56, No. 13, Mar. 31, 1958, pp. 73-76, the BP isomerization process as described in Hydrocarbon Processing, Vol. 45, No. 8, Aug. 1966, pp. 168-170, and the liquid phase isomerization process described in Hydrocarbon Processing, Vol. 42, No.7, July 1963, pp. 125-130.

Thus, in the process of the present invention, it is preferred to use a hydroisomerization catalyst which is essentially free of halogenated aluminum. Catalysts comprising crystalline aluminosilicates, such as molecular sieves, mordenite, and layered crystalline aluminosilicates, are particularly preferred. It is preferred to use one or more hydrocarbon components with the crystalline aluminosilicate. Palladium and platinum are preferred hydrogenation components. Preferred catalysts comprising crystalline aluminosilicate and a hydrogenation component such as palladium or others are described in patent applications Ser. Nos. 776,733 and 839,999, which applications are incorporated by reference into the present patent application, particularly those portions of the aforeidentified applications disclosing catalyst compositions. Preferred aluminosilicate-containing catalysts for use in the isomerization zone include catalysts comprising a layered clay-type aluminosilicate cracking component, with 0.01 to 2.0 weight percent, based on said cracking component and calculated as the metal, of a hydrogenating component selected from platinum, palladium, iridium, ruthenium and rhodium, and also with 0.01 to 5.0 weight percent, based on said cracking component and calculated as the metal, of a hydrogenating component selected from tungsten and chromium. Particularly preferred hydroisomerization catalysts are those as described above wherein the hydrogenating components are palladium and chromium. In the present specification, oxides and other compounds of metals are to be considered as included in reference to a metal simply as an element, i.e., chromium includes the use of chromium in compound forms such as chromium oxide.

Preferred catalysts for use in the C disproportionation reaction zone are catalytic masses having a component with alkane dehydrogenation activity and a second component with olefin disproportionation activity, for example, catalytic masses comprising a Group VIII metal component and a Group VIB metal component. Particularly preferred C disproportionation catalysts include catalytic masses comprising a noble metal on a refractory support and a Group VIB metal or metal compound on a refractory support, for example a catalytic mass comprising platinum on alumina and tungsten or tungsten oxide on silica. Preferred temperatures for the disproportionation of butanes using the above-indicated catalytic masses are between about 400850F. and more preferably between 650-799F. Pressure maintained in the disproportionation reaction zone is preferably between atmospheric and 2,500 psia, and still more preferably between and 1,500 psia. In addition to the preferred relatively low temperature for hydrocarbon disproportionation, we have found that it is preferable to carry out the disproportionation reaction in the presence of no more than a few weight percent olefins, preferably less than 5 weight percent olefins. Preferred conditions for the disproportionation of saturated hydrocarbons such as butane or hexane are further discussed in commonly assigned applications Ser. Nos. 3,303 and 3,306, the disclosures of which applications are incorporated by reference into the present application.

In a commonly assigned application of Robert P. Sieg, filed the same day as the present application and titled Hexanc Conversion,. a similar process is described wherein a C -rich hydrocarbon fraction is isomerized, preferably followed by C disproportionation and C disproportionation. The present application is directed to C isomerization followed by C disproportionation and, among other features, is based upon our surprising finding that very high yields of isopentane are obtained using the C isomerization-C disproportionation combination, with the C disproportionation zone eliminated.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flow diagram illustrating preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWING Referring now more particularly to the drawing, a C -rich hydrocarbon stream is fed via lines 1 and 3 to isomerization zone 4. The C fraction or cut can be obtained from the effluent from a catalytic reforming process and advantageously upgraded in the process of the present invention to isopentane. However, the process combination of the present invention has particular application to straight run hydrocarbon C -rich fractions containing organic sulfur compounds, usually in an amount between about 5 ppm and 300 ppm, calculated as sulfur by weight.

The C -rich hydrocarbon'fraction is isomerized in the presence of hydrogen using a hydroisomerization catalyst which preferably comprises a crystalline aluminosilicate together with a hydrogenation component such as palladium or platinum. Preferred operating conditions for the C isomerization include a hydrogen gas rate in the range of 1,000 to 5,000 SCF/b., preferably 1,500 to 2,000 SCF/b.; space velocities in the range of about 0.1 to 20 liquid volumes per hour per volume of catalyst, preferably 1.0 to 5.0 LHSV; temperatures in the range of about 200-800F., preferably 250 to 750F.; and pressures within the range of atmospheric to 3,000 psig, preferably in the range of 500-800 psig.

In addition to isomerizing normal hexane in isomerization zone 4, normal pentane derived from disproportionation zone 16 is also isomerized in zone 4. As shown in the drawing, normal pentane from the disproportionation zone is recycled via line 2 and then introduced via line 3 to the isomerization zone. After stripping hydrogen sulfide from the isomerization reaction zone effluent and/or removing hydrogen sulfide by other methods, the isomerization effluent hydrocarbons are fed via lines 5 and 7 to fractionation zone 8.

Fractionation zone 8 typically consists of 3 to 8 distillation columns used to separate the various components obtained both from isomerization in zone 4 and disproportionation in zone 16, according to the preferred embodiment illustrated in the drawing. As indicated previously, the fractionation zone can have a varying number of distillation columns, and it is preferred to use common fractionation facilities for at least part of the separation of effluent hydrocarbons from isomerization zone 4 and disproportionation zone 16. it is particularly preferred to carry out the fractionation of normal pentane from C alkanes in the same fractionation column for effluent hydrocarbons from disproportionation zone 16 and isomerization zone 4.

C alkanes are removed from the fractionation zone via line and fed to disproportionation zone 16 via line 15. The C hydrocarbons are disproportionated at least in part to obtain normal pentane, propane and hexanes. Effluent hydrocarbons including normal pen tane are removed from disproportionation zone 16 via line 17 and passed via lines 6 and 7 to fractionation zone 8.

1n fractionation zone 8 normal pentane is separated. The normal pentane is passed via line 2 and line 3 to isomerization zone 4.

1n isomerization zone 4, the normal pentane derived from disproportionation zone 16 is isomerized to isopentane which is ultimately fractionated from the isomerization zone effluent hydrocarbons and recovered as a product withdrawn via line 18.

Preferably the feed to disproportionation zone 16 is a mixture of iC, and nC, withdrawn via line 15 from frac' tionation zone 8. However, a portion or substantially all of the iC, can be withdrawn from zone 8 via line 9. Instead of upgrading the iC in disproportionation zone 16, the separately withdrawn iC, in line 9 can be fed to an alkylation plant for reaction with olefins to produce high-octane gasoline.

Propane and other light gases formed in isomerization zone 4 and also in disproportionation zone 16 are removed from the effluent hydrocarbons from these two respective zones by separation in zone 8.

TABLE I.ISOMERIZATION OF SYNTHETIC NAPHTHA Preferably, common fractionation facilities are used to separate the propane and other light gases generated in disproportionation zone 16 and in isomerization zone 4, particularly when the isomerization is carried out at a high temperature, for example in excess of 700 or 750F., so as to generate substantial amounts of propane and other light hydrocarbons. When the isomerization zone is operated at relatively mild conditions, for example below 700F., and with only 1 or 2 percent or less weight percent propane produced in isomerization zone 4, depropanizing the effluent hydrocarbons from the isomerization zone could advantageously be carried out separate from the depropanizing of the effluent hydrocarbons from disproportionation zones 12 and 16.

Particularly preferred temperatures for the isome rization zone using the preferred Pd-Cr-crystalline.

clay-type layered aluminosilicate catalyst are about 650750F. At these temperatures for this catalyst, we have found high isomerization yields and high conversion of hexane (see Table I hereinbelow). Isomerization at these preferred conditions results in surprisingly high yields of iC when carried out in cooperation with C, disproportionation (see Table III hereinbelow).

Some heavier hydrocarbons, i.e., C-,+ hydrocarbons, are formed in disproportionation zone 16. These heavier hydrocarbons are withdrawn from fractionation zone 8 via line 20. The C hydrocarbons can be advantageously used as a feedstock for catalytic reforming to produce high-octane gasoline, for example by reforming using a platinum-rhenium on alumina catalyst. The C,+ hydrocarbons alternately can be passed at least in part via lines 22, 2, and 3 to isomerization zone 4. The C hydrocarbons are suitable feedstock for isomerization and cracking to lower hydrocarbons including normal butane and isopentane.

EXAMPLES Example 1 A C -rich fraction was desulfurized from 100 ppm S to less than 0.1 ppm S under the following reaction conditions:

T, "F. 700 P, psig 800 LHSV 1.0

Catalyst composition: Pd-Cr-Layered crystalline aluminosilicate catalyst as in Example 1, a C -rich fraction free of sulfur'was isomerized at 800 psig, LHSV 1.0 and hydrogen rate 17,000 SCF/bbl. of feed, with the results as shown in Table 1.

Catalyst temperature, F.

0. 18 r (l. 42 0. 28 0. 110 1.111 11.10 0.00v 1.34 ll-(14 f A (1.611 2.12 Total cracked prod, wt.

percent. 0. 40 0.53 (l. 03 0. 77 0.118 1. 33 1. 87 2. 74 3. 60 5. 36 7. 4] J. 30 13. U2 IS0C5 15.05 10. 37 17. 30 111.117 2.07 25. 41 28. 48 30. X0 32. 43 30. 71 30. 35 29. 13 211. 34 Il-Cs 50 35. 75 35. 00 34. 10 32. 05 30. 13 27. 37 25. 03 22. 71 20. 1.). 40 17. 44 17.33 17.03 17. 26 2,2-dimcthyl butane 0. 40 0. (i1 0. 03 1. 3!! 2. ll 2. 00 3. 52 4. 20 4. 27 5. 31 5. 56 5. 40 4. 00 2,3-(limothyl bu 1121110.. 0. 75 1.00 1.33 1. 1. ill! 2. 25 2. 40 2. 48 2. 50 2. 60 2. (i7 2. 54 2. 30 2-mothyl pentane... .10 13.17 13. 33 14.44 15. 33 15. 04 15. 38 14.117 14. 00 13. 04 13. 41 13. 51 13. 72 12.11!) 12. 23 li-mothyl pentane 11. 47 10. 22 5). 11!] 10.23 10. (iii 10. 83 10. 73 10. 52 10. I!) 0. K!) 0. 46 0. 62 ll. 60 (I. 28 3. ll 0 21. 54 17. 20 15. 74 14.47 13.17 11. 08 10. 02 ll. 08 0. 45 l. 24 3. .10 i1. 22 I. 12 El. ()0 H. 44 Methyl (3yC1OI)Ull1.11l1l. r 2. 47 4. 74 5. 03 1i. l!) 0. 08 (i. 72 7.07 0. 28 5. 64 5. 22 4. (i4 4. 73 3. 00 3. 73 2. 42 Benzene. ().7!| (Iyulohoxanu 5. 33 3. 73 3.03 2. 03 1. 5| 1. 21 1.28 1.22 0. 32 0 82 0.136 0. 83 0. 40 1.05 (J. 20

Example 3 The data tabulated in Table 11 below illustrate the results obtained in disproportionating normal butane by contacting normal butane with an alkane disproportionation catalyst mass under the following conditions:

Volume of Catalyst in Reactor: 9 cubic centimeters (cc.)

Type of Catalyst:

2 cc. of 0.5 wt.% Pt; 0.5 wt.% Re; 0.5 wt.% Li on A1 7 cc of 8.0 wt.% W0 on SiO Both types of catalyst particles were 28 to 60 Tyler mesh size.

Operating Conditions:

Temperature: 650, 700, 750, 800, 875 F. Pressure: 900 psig Feed rate: 9 cc./hour Successive runs, of several hours each with no regeneration in between, were made at the temperatures specified, except that the catalyst was reactivated by flushing the catalyst overnight with hydrogen before the run at 875 F.

As can be seen from the data tabulated in Table II, the ultimate yield of C decreases considerably in moving from particularly preferred temperatures below 800F. to temperatures in excess of 800F. as, for example, temperatures as high as 875F., where the ultimate yield of C drops to about 42% vs. approximately 57% at 750F. More importantly, the yield of nC is All olefins analyses are from an approximate chromatographic analy- 1 The decrease in branching with decreasing temperature indicates the process of the present invention is more selective for pure disproportionation without isomerization at lower temperatures. This attribute is important when it is desired to produce n-parafi'ms, as, for example, in wax production.

N.M. not measured because products were hydrogenated prior to analysis.

Example 4 Table III below tabulates the surprisingly high yield of iC (68 wt. percent) with no C disproportionation zone. Table 111 is based on laboratory data for isomerization and C disproportionation and calculations based on the indicated recycle from fractionation zone 8.

TABLE IIIr-NO (1a DISPROPORTIONATION ZONE C (lispropor- Fri-sh Fresh lrml. lsomerization zone tionation zone Fractionation zonv 10((1 to 10((1 to (list., (4 (lisp. fralz. wt. Feed Effluent Fer-d Effluent Efiluent Recycle Zone Zone percent C 7. 52 41. 07 Isobutane. 1. 91 292. 37 247. 05 Isobutene.. 1. 47 {Butane 2.20 112. 34 $2. sopentane. 85.02 4. 86 n-Pentane 104'15 1 50.77 8. 2,2-dimethylbutane 2 3-d1methylbutane 2-methylpentane.. 280. 49 244. 64 13. 74 3-methylpentane r-Htfxkane yo 0 exane 1. 65 Methyleyelopentane 2062 1 11.55 C7+ 0. 08

I Numbers are qualitative only and do not represent exact mutt-rial balance for steady-slate ODIHlllOlI.

seen to be greater at temperatures'between 700 and 800F. than at higher temperature such as 875F.

TABLE 11 Weight Product Yields at Various Operating Although various embodiments of the invention have been described, it is to be understood that they are meant to be illustrative only and not limiting. Certain features may be changed without departing from the spirit or scope of the present invention. It is apparent that the present invention has broad application to combined C C alkane isomerization and C disproportionation to produce isopentane. Accordingly, the invention is not to be construed as limited to the specific embodiments or examples discussed, but only as defined in the appended claims or substantial equivalents of the claims.

What is claimed is:

l. A process for producing isopentane which comprises:

a. isomerizing a C -rich hydrocarbon fraction containing C and C hydrocarbons in an isomerization zone to obtain at least isopentane and C alkanes;

b. fractionating the isopentane from the C, alkanes to obtain an isopentane product;

c. disproportionating at least a portion of the C alkanes in a C disproportionation zone by contacting the C alkane with a catalyst comprising a Group VIII metal or metal compound and a Group VIB metal or metal compound at a temperature between 400F. and 850F. to obtain at least npentane and C hydrocarbons; and

d. isomerizing the n-pentane to iso-pentane in the isomerization zone.

2. A process in accordance with claim 1 wherein the C -rich hydrocarbon feed to the isomerization zone contains at least ppm sulfur present as organic sulfur compounds and the isomerization is carried out using a sulfactive isomerization catalyst at conditions sufficient to convert the organic sulfur compounds to H 8 and hydrocarbons, and H 8 is separated from the C alkanes from the isomerization zone before the 3 al kanes are fed to the disproportionation zone.

3. A process in accordance with claim l'wherein common fractionation facilities are used at least in part for effluent hydrocarbons from the isomerization zone and effluent hydrocarbons from the C. disproportionation zone.

4. A process in accordance with claim 3 wherein the same fractionation column is used for the fractionation of normal pentane from C alkanes present as a mixture in effluent hydrocarbons from both the isomerization zone and the C disproportionation zone.

5. A process in accordance with claim 1 wherein the C -rich hydrocarbon stream fed to the isomerization zone is a straight run fraction obtained by fractionating a C -rich cut from crude oil.

6. A process in accordance with claim 1 wherein the catalyst used in the isomerization zone is substantially free of halogenated aluminum.

7. A process in accordance with claim 1 wherein the isomerization catalyst comprises palladium or platinum and a crystalline aluminosilicate material.

8. A process in accordance with claim 1 wherein the isomerization catalyst comprises 0.05 to 5.0 weight percent palladium and 0.05 to 5.0 weight percent chromium on a layered clay-type crystalline aluminosilicate material.

9. A process in accordance with claim 1 wherein the disproportionation reaction is carried out at a temperature between 400 and 850F. using a catalyst comprising a noble metal on a refractory support and a Group VIB metal compound on a refractory support.

10. A process in accordance with claim 1 wherein the disproportionation reaction comprises contacting the C alkanes with a catalytic mass comprising platinum on alumina and tungsten or tungsten oxide on silica at a temperature between about 650 and 850F. and a pressure between about psia and 1,500 psia.

11. A process in accordance with claim 10 wherein the olefin concentration in the disproportionation reaction zone is maintained below about 5 volume percent.

12. A process for producing isopentane from C hydrocarbons which comprises:

a. isomerizing a C -rich hydrocarbon stream containing C and C hydrocarbons and between 5 and 500 ppm organic sulfur compounds in an isomerization zone by contacting the C -rich hydrocarbons with a sulfactive isomerization catalyst at a hydrogenpartial pressure between about 100 and 1,500 psig and a temperature between about 200F. and 800F. to obtain a C rich effluent stream containing less than 0.1 ppm sulfur present as organic sulfur compounds,

b. disproportionating at least a portion of the C -rich effluent stream by contacting the C hydrocarbons with a catalyst comprising platinum on a refractory support and a Group Vl"B metal or metal oxide on a refractory support at a temperature between 400 and 850F. to obtain a hydrocarbon stream comprising propane, normal pentane and C hydrocarbons,

c. isomerizing at least a portion of the normal pentane from the C disproportionation in the isomerization zone to obtain isopentane. 

2. A process in accordance with claim 1 wherein the C6-rich hydrocarbon feed to the isomerization zone contains at least 5 ppm sulfur present as organic sulfur compounds and the isomerization is carried out using a sulfactive isomerization catalyst at conditions sufficient to convert the organic sulfur compounds to H2S and hydrocarbons, and H2S is separated from the C4 alkanes from the isomerization zone before the C4 alkanes are fed to the disproportionation zone.
 3. A process in accordance with claim 1 wherein common fractionation facilities are used at least in part for effluent hydrocarbons from the isomerization zone and effluent hydrocarbons from the C4 disproportionation zone.
 4. A process in accordance with claim 3 wherein the same fractionation column is used for the fractionation of normal pentane from C6 alkanes present as a mixture in effluent hydrocarbons from both the isomerization zone and the C4 disproportionation zone.
 5. A process in accordance with claim 1 wherein the C6-rich hydrocarbon stream fed to the isomerization zone is a straight run fraction obtained by fractionating a C6-rich cut from crude oil.
 6. A process in accordance with claim 1 wherein the catalyst used in the isomerization zone is substantially free of halogenated aluminum.
 7. A process in accordance with claim 1 wherein the isomerization catalyst comprises palladium or platinum and a crystalline aluminosilicate material.
 8. A process in accordance with claim 1 wherein the isomerization catalyst comprises 0.05 to 5.0 weight percent palladium and 0.05 to 5.0 weight percent chromium on a layered clay-type crystalline aluminosilicate material.
 9. A process in accordance with claim 1 wherein the disproportionation reaction is carried out at a temperature between 400* and 850*F. using a catalyst comprising a noble metal on a refractory support and a Group VIB metal compound on a refractory support.
 10. A process in accordance with claim 1 wherein the disproportionation reaction comprises contacting the C4 alkanes with a catalytic mass comprising platinum on alumina and tungsten or tungsten oxide on silica at a temperature between about 650* and 850*F. and a pressure between about 100 psia and 1,500 psia.
 11. A process in accordance with claim 10 wherein the olefin concentration in the disproportionation reaction zone is maintained below about 5 volume percent.
 12. A process for producing isopentane from C6 hydrocarbons which comprises: a. isomerizing a C6-rich hydrocarbon stream containing C4 and C5 hydrocarbons and between 5 and 500 ppm organic sulfur compounds in an isomerization zone by contacting the C6-rich hydrocarbons with a sulfactive isomerization catalyst at a hydrogen partial pressure betWeen about 100 and 1,500 psig and a temperature between about 200*F. and 800*F. to obtain a C4-rich effluent stream containing less than 0.1 ppm sulfur present as organic sulfur compounds, b. disproportionating at least a portion of the C4-rich effluent stream by contacting the C4 hydrocarbons with a catalyst comprising platinum on a refractory support and a Group VIB metal or metal oxide on a refractory support at a temperature between 400* and 850*F. to obtain a hydrocarbon stream comprising propane, normal pentane and C6 hydrocarbons, c. isomerizing at least a portion of the normal pentane from the C4 disproportionation in the isomerization zone to obtain isopentane. 